Index: firmware/App/Services/SystemCommMessages.c
===================================================================
diff -u -r07a5add2dff254f7be3699e4efac2b99d3554847 -r9a9d04b84f4345fca87fb14d26f09d497b08aae8
--- firmware/App/Services/SystemCommMessages.c	(.../SystemCommMessages.c)	(revision 07a5add2dff254f7be3699e4efac2b99d3554847)
+++ firmware/App/Services/SystemCommMessages.c	(.../SystemCommMessages.c)	(revision 9a9d04b84f4345fca87fb14d26f09d497b08aae8)
@@ -118,7 +118,7 @@
     _enable_IRQ();
     if ( TRUE == ackReq )
     {
-        msg.hdr.seqNo |= MSG_ACK_BIT;
+        msg.hdr.seqNo *= -1;
     }
 #endif
 
@@ -180,8 +180,7 @@
     // create a message record
     blankMessage( &msg );
     // send ACK back with same seq. #, but w/o ACK bit
-    msg.hdr.seqNo = message->hdr.seqNo;
-    msg.hdr.seqNo &= ~MSG_ACK_BIT;
+    msg.hdr.seqNo = ( message->hdr.seqNo < 0 ? message->hdr.seqNo * -1 : message->hdr.seqNo );
     // ACK messages always have this ID
     msg.hdr.msgID = MSG_ID_ACK;